1. Field of the Invention
This invention relates to a break detection system for a processing line in which strip material is being payed out from a payoff reel to a rewind reel.
2. Description of the Prior Art
In the continuous processing of materials, it is imperative that the operator know as quickly as possible when a break occurs in the material. This is demanded in some industrial applications because a break may cause damage to the processing equipment per se, but even where this is not the case, it is still important to know when a break occurs in order to mitigate the economic losses occurred by prolonged down time.
In the processing of strand material, U.S. Pat. No. 3,429,491 to Windley for "Break Detector and Shut Down Means", Windley detects the breakage of one or more filaments by reason of the fact that there is a loss in tension in the filaments which is a function of the power output of the take up or pulling motor. The decrease in motor power is sensed by a Hall effect device which operates through various relay contacts to shut down the power to the pay out motor.
U.S. Pat. No. 3,863,241 to Kamiyamaguchi et al. entitled "Yarn Break Detector Utilizing a Sensor for Sensing the Yarn Static Electricity" utilizes a collecting electrode in contact with the moving yarn to detect the static electricity generated by the moving material, and positive pulses are continuously generated. When the yarn is broken, the charges disappear, and negative pulses are generated which are then processed to produce the alarm pulse signal.
In the processing of metals, the techniques have been somewhat different. One analog approach which has been used is to compare the entry strip speed with the delivery strip speed by utilizing the entry and delivery billy roll speeds as modified for the nominal mill draft. These analog systems have never proven to be fully reliable because of changes in draft during rolling, as well as the slippage of the billy rolls in contact with the moving material.
The systems presently in use for strip break detection permit a reel device to go into speed limit and then detect when that limit has been reached. In a processing line tension is placed on the material by the combined effect of the rewind reel pulling in one direction and the payoff reel yieldingly pulling in the opposite direction. When a break occurs, the rewind reel continues to pull in the same direction but the payoff reel, now experiencing no opposing pull, winds in the opposite direction so that speed limit for the payoff reel occurs at essentially zero speed. This scheme is reliable but it requires too long for the reels to attain speed limit.